The present invention relates generally to performance characteristics of integrated circuits and, more particularly, to a method for specifying performance characteristics of integrated circuits to facilitate manufacturing while still ensuring proper operation of the integrated circuits by defining acceptable boundary areas within which selected performance characteristics must occur.
Manufacturers of integrated circuits (IC's) must satisfy certain performance characteristics specified by users of the IC's who rely on the specifications to ensure proper operation of equipment incorporating the IC's. Typically, an IC user issues an engineering specification detailing the required operating characteristics and parameters for an integrated circuit. The engineering specification contains, for example maximum and minimum input and output voltages, output capacitance and maximum unpowered current leakage. Another significant performance characteristic usually specified by the IC user is the slew rate or rate of change of output signals generated by an integrated circuit.
While the IC specification method of the present invention is generally applicable for any integrated circuits, it will be described with reference to a transmitter driver for a data bus for which the method was developed and has been successfully performed. The transmitter driver provides controlled slew rate drive for a data bus of a data communications system. The noted transmitter driver was developed for use in motor vehicle multiplex communications systems which intercouple various accessories, accessory switches, sensors, displays and the like over data buses to reduce the physical wiring within a motor vehicle.
The signal transition characteristics of the transmitter driver including the signal slew rate must satisfy conflicting demands and become increasingly critical at higher data transmission rates. Thus, the transmitter driver must operate at a speed sufficient to allow maximum data transfer rates while minimizing induced electromagnetic interference (EMI) on the data bus. Excessive EMI on the data bus may result in unexpected vehicle faults causing unpredictable failures. Further, operation of other system components which are designed around a particular data transmission rate may be effected by deviations from the transmitter driver specification.
To prevent such problems, the IC manufacturer is provided with a detailed listing of the required transition characteristics of the transmitter driver. In order to meet the specifications for an integrated circuit, the IC manufacturer must normally test each individual performance characteristic specified to ensure compliance. Such testing requires substantial amounts of time and hence increases the cost of the IC. Further, meeting each individual performance specification can add to the cost of the IC since actions taken to meet one specification may detract from another specification which also must be met.
It is thus apparent that a need exists for an improved method of specifying the performance characteristics of an integrated circuit which reduces manufacturing and testing costs yet ensures proper operation of resulting integrated circuits.